1. Field of the Invention
This invention relates to a device for blood plasma preparation for a variety of analytical assays. More particularly, the present invention pertains to a blood collection device comprising a thixotropic polymeric polyester gel and an anticoagulant formation. The device of the present invention is most preferably used in nucleic acid testing, which use amplification technologies including, but not limited to, polymerase chain reaction (PCR), branched DNA (bDNA) and nucleic acid sequence based amplification (NASBA).
2. Description of Related Art
New amplification technologies, such as polymerase chain reaction (PCR), branched DNA (bDNA), and nucleic acid sequence based amplification (NASBA), allow researchers to monitor the levels of infectious agents in plasma. Studies have demonstrated that the number of extracellular HIV RNA viral copies, or viral load, is a surrogate marker for the progression of the HIV infection. Scientific research has shown that HIV replication occurs throughout the life of the infection. After the initial infection, the HIV viron enters susceptible cells, replicates rapidly creating billions of copies of the HIV viral RNA soon after infection. Although the HIV RNA viral load varies across the patient population, the disease follows a specific progressive pattern within each patient. Therefore, monitoring the HIV RNA viral load of HIV infected patients can be used to manage the disease. In addition, the patients' response to approved drugs, new drugs and combination drug therapies can be evaluated by monitoring the patient's HIV RNA viral load.
In addition to the HIV virus, there are a number of other infectious diseases that would benefit from viral load monitoring, such as the Hepatitis C virus.
Measurements of the viral load are determined by using polymerase chain reaction (PCR), branched DNA (bDNA), and other amplification techniques. The quality and consistency of the sample is critical to obtaining optimal test results using these technologies. There are a number of variables that influence the sample quality, such as the collection method, centrifugation time, sample preparation technique, transport to the test laboratory, contamination with cellular materials, and the like.
Numerous sample types have been evaluated for nucleic acid testing, including whole blood, serum and plasma. Studies have shown that the HIV viral load is stable for up to 30 hours in a whole blood sample using EDTA as the anitcoagulant. The clotting process required to produce serum can artificially lower the viral load by trapping viral particles in the resulting clot. Although the preferred sample type is plasma, the preparation of a plasma sample may adversely affect the outcome of the amplification process. For example, if the plasma sample remains in contact with the red blood cells, heme molecules from the hemoglobin contained within red blood cells will interfere with PCR amplification if hemolysis occurs. In addition, since the half-life of the neutrophils is approximately 24 hours in a blood collection tube, and as the neutrophils begin to die they release granules which contain myeloperoxidase into the sample, and since myeloperoxidase causes reduction in the viral load, this is also another factor that supports the need to sequester the plasma sample away from blood cells.
A further example of the difficulties associated with current plasma preparation is the fact that blood collection tubes may contain a liquid anticoagulant to prevent clotting of the sample. A liquid anticoagulant may dilute the viral load value per volume of sample. Therefore, the viral load value may be below the threshold of detection.
Commercially available blood collection products such as (all sold by Becton Dickinson and Company, Franklin Lakes, N.J. and all registrations and trademarks are of Becton Dickinson and Company) VACUTAINER Brand Hematology tubes, Catalog nos. 367650-1, 367661, 6405, 6385, 6564, 367653, 367665, 367658, 367669, 6450-8, 6535-37, 367662; VACUTAINER Brand K.sub.2 EDTA tubes catalog no. 367841-2, 367856, 367861; VACUTAINER Brand PST tubes catalog nos. 367793-4, 6698, 6595, 6672; VACUTAINER Brand CPT tubes catalog nos. 362753, 362760-1; VACUTAINER Brand SST tubes catalog nos. 367782-89, 6509-17, 6590-92; and VACUTAINER Brand ACD tubes catalog nos. 367756, 364012, 4816; may be used for nucleic acid testing. However, these commerically available products may not consistently provide a sample of good integrity and therefore may not provide consistent and adequate amplification results.
Therefore, a need exists to provide a standard device designed to collect, process, and transport plasma samples for use with amplification technologies. Most preferably, the device should be able to assist in standardizing specimen handling, provide a closed system, isolate the plasma from the cellular components, produce minimal plasma dilution, and minimize interference with the nucleic acid testing.